The earth has had mass extinctions only five times in the past 540 million years, and some scientists think we are heading into the sixth. It may not happen for a few centuries, but that doesn't mean it's not a crisis.
In each of the five past catastrophic extinctions, more than 75 percent of all animal species on earth were wiped out. The present deep declines in the populations of many animal species, including frogs, tigers, and some fish and birds, have alarmed many scholars in the life sciences.
A group of scientists at the University of California at Berkeley applied new statistical methods to a new generation of fossil databases and concluded that the current rate of extinction is far above normal.
Humans have pushed species toward extinction by over-fishing, over-hunting, de-forestation and population growth that destroyed animal habitats. Global warming could exacerbate the push, and add unforeseen complications.
"The current rate and magnitude of climate change are faster and more severe than many species have experienced in their evolutionary history," Anthony Barnosky, a paloecologist who has studied the rise and fall of species over the past few million years is quoted as saying in a New York Times story by Carl Zimmer. Barnosky is also the lead author of a study published in Nature, which suggests the sixth mass extinction could happen within as little three to 22 centuries.
While ecosystems change and extinctions are normal, Barnosky says in a Berkeley news story by Robert Sanders, past climate change, such as cooling at the beginning of glacial periods and the warming as interglacial periods began, happened over thousands of years. The current warming is ten times faster.
Animals have been known to change their migrations patterns to adapt to climate change, but as the Times story points out, changes caused by human development and activity may limit their ability to shift their geographical range. Some animals adapt by changing their behavior, but that too can have unforeseen consequences. For instance, the Times story notes, melting sea ice makes it harder for polar bears to hunt for seals, their dietary staple. So they spend more time on land and hunt for goose eggs, which bodes ill for the geese.
According to a Berkeley news story, biologists estimate that at least 80 mammal species have become extinct in the last 500 years. Barnosky says it's not too late to devote resources and legislation to foster biodiversity and conservation of endangered animal and plant species.